(1) Field of the Invention
The present invention relates to a precursor for the synthesis of Cimetidine which has an action of controlling secretion of acid in the stomach based on the histamine H.sub.2 receptor antagonism and is valuable as a drug for treating gastric ulcer, and a process for the preparation of this precursor.
(2) Description of the Prior Art
Imidazole derivatives such as 4-hydroxymethyl-5-methylimidazole disclosed in Japanese patent application laid-open specification No. 142271/81, 4-(2-aminoethylthio)-5-methylimidazole disclosed in Japanese patent application laid-open specification No. 42661/72 and [(4-methyl-5-imidazolyl)methylthioethyl]-S-methylisothiourea disclosed in Japanese patent application laid-open specification No. 75574/74 are mainly known as the precursor for the synthesis of Cimetidine and Cimetidine can be derived from these imidazole derivatives. As the precursor that can be converted to Cimetidine by forming an imidazole ring at the final stage, there can be mentioned N-cyano-N'-2-(2,3-diketobutylthio)ethyl-N"-methylguanidine disclosed in Spanish Pat. No. 455,991 [Chemical Abstracts, 89, 146904 I, 1978]. Diacetyl which is the starting material for the synthesis of this precursor has an offensive smell and causes a problem concerning the working environment, and the yield of the precursor is not always high.